As protective tissue and exchange boundary, the skin is rapidly renewed throughout a lifetime. Passing time inevitably results in aging of the skin. Premature aging may even occur as a consequence of multiple environmental attacks. As an interface with the outside environment, skin is constantly subjected to damage resulting from all kinds of physicochemical attacks: temperature change, humidity, light, pollution, etc. The skin cells age, become senescent and die after about 80 divisions. Throughout this process the skin loses its thickness and elasticity, causing the onset of wrinkles, and it also loses its protective role in particular against daytime UV radiation. It can also have irregular pigmentation (age spots).
The molecular causes of skin aging involve all the compartments of the skin. As in other tissues, some proteins induced by stress play a central protective role, in particular the chaperone proteins, which allow suitable folding of proteins and correct the defects of this folding, and proteases, which degrade chemically-deteriorated or misfolded proteins The process of translation and folding gradually becomes less efficient as cells age, thereby resulting in the occurrence of and increased sensitivity to accidental oxidising modifications and glycations. Reactive oxygen species alter the amino acids (in particular cysteine, histidine, methionine, tyrosine and tryptophan) and protein backbones. They also cause upstream deterioration of processes which lead to the synthesis of new proteins.
The accumulation of protein aggregates during the aging process progressively submerges the machinery controlling the quality of cell proteins. This aging of the skin entails degradation of the extracellular matrix both at the epidermal and dermal layers, leaving visible signs of aging on the surface of the skin and modifying the physical properties thereof.
The overall consequence is also a deterioration of normal enzymatic activity and an aggregation of whole proteins, leading to visible signs such as irregular dryness, irregular pigmentation, deep wrinkles, waxy and/or parchment complexion, sagging of the skin, etc.
Three processes enable the cells to overcome aging: neo-synthesis, repair and degradation followed by re-synthesis. Over the long term the last two processes are essential since they allow cell rejuvenation.
There is therefore a need and strong demand for novel cosmetic care products to combat aging of the skin.